(Revised Abstract) DESCRIPTION (provided by applicant): The Mass Spectrometry Shared Resource provides essential services to Cancer Center members whose research requires accurate structure determination of a variety of different molecules. Services currently provided by the Shared Resource include operatorassisted low- and high-resolution electron ionization (EI), chemical ionization (CI), and electrospray ionization (ESI), tandem mass spectrometry (MS/MS), and LC-MS analyses. The Shared Resource also provides expert assistance to Cancer Center members in the selection of instruments and analytical methods to solve specific problems. A major expansion of the Shared Resource is planned in order to provide protein analysis services to Cancer Center members. Acquisition of state-of-the-art MALDI-TOF and Q-TOF instruments is under way, expert advice and consultation will be provided by a new Director, and sample processing services will be provided so that Cancer Center members can submit sample isolates directly without concern for instrument compatibility. These new services will extend the same high-quality analytical support to the study of proteins that has been provided for many years to investigations of small molecules.